Radio works intermittently

My radio system is temperamental. It works when it wants to. The cassette player worked then stopped for a while started up again then nothing. When it does not work the cassette is stuck until the cassette player works again and will release it. The CD player used to work with all six in there then when I took them all out to put new ones in it still thought there was a CD in that slot. Then the couple of CD's that are in there only works when it wants to, but 99% of the time I get an error message for the CD player. I can turn the radio on by the by both buttons. Sometimes the radio can be on and it is all silence and then all of a sudden there is a loud crack that comes from the speakers and the radio will start to work. I had to have the radio off before turning off the car when it is working. So that the next time I get in; I start the car and wait about a minute before driving off, and do not turn the radio on until at least two miles down the road. That seems to help but not often. I have driven one and half hours straight before the radio came on and I got to enjoy the radio for the last fifteen minutes of my trip. What can I do to check this out?